The present invention relates to a driving method of a plasma display panel, and more specifically to a driving method of a plasma display panel of an alternate current discharge type and a matrix display scheme.
A first example of a conventional plasma display panel and a method for driving the same will be described with reference to the drawings. FIG. 12 is a partial sectional view of the conventional plasma display panel. The conventional plasma display panel includes two insulating substrates 1a and 1b formed of glass and constituting a front plate and a back plate.
On the insulating substrate 1a, transparent scan electrodes 2 and sustain electrodes 3 are formed, and trace electrodes 4 are formed to lay over the scan electrodes 2 and the sustain electrodes 3 to reduce a resistance value of these electrodes. In addition, a first dielectric layer 9 is formed to cover the scan electrodes 2 and the sustain electrodes 3. Furthermore, a protection layer 10 of magnesium oxide or another is formed to protect the dielectric layer 9 from an electric discharge.
On the insulating substrate 1b, data electrodes 5 are formed to extend orthogonally to the scan electrodes 2 and the sustain electrodes 3. A second dielectric layer 11 is formed to cover the data electrodes 5. On the second dielectric layer 11, a partition 7 is formed to extend in the same direction as that of the data electrode and to confine display cells which are a unit of display. Furthermore, a phosphor layer 8, which converts a ultraviolet radiation generated by an electric discharge in an electric discharge gas, to a visible light, is formed on a side surface of the partition 7 and on a surface of the dielectric layer 11 on which the partition 7 is not formed.
Furthermore, a space sandwiched between the insulating substrates 1a and 1b and confined by the partition 7 constitutes an electric discharge space filled up with an electric discharge gas which is formed of helium, neon, xenon and a mixed gas of those gases.
In the plasma display panel constituted as mentioned above, a surface electric discharge 100 is generated between the scan electrode 2 and the sustain electrode 3.
FIG. 13 is a diagram of illustrating an electrode location in the conventional plasma display panel. One display cell 12 is formed on each intersection between one scan electrode 2 and one sustain electrode 3 and one data electrode 5 extending orthogonally to these electrodes. The scan electrodes 2 are individually connected to a scan driver integrated circuit (IC) 21 so that a scan voltage pulse is individually applied to each scan electrode. All the sustain electrodes 3 are electrically connected in common to a sustain circuit 22 at a panel end or on a driving circuit, so that only a common waveform is applied to the sustain electrodes. In addition, the data electrodes 5 are connected to a data driver integrated circuit (IC) 23 so that a data pulse can be individually applied to each data electrode.
Now, various selective display operations of the display cell will be described. FIG. 14 is a timing chart for illustrating voltage pulses applied to various electrodes in a first conventional driving method. In addition, FIG. 15 is a diagram for illustrating a wall electric charge within the display cell during a selection period B in the first conventional driving method. In FIG. 14, a period A is a preliminary electric discharge period for facilitating generation of an electric discharge in a succeeding selection period, and a period B is a selection period for on-off selecting the luminescence of each display cell. A period C is a sustain period for causing an illuminant electric discharge in all the selected display cells, and a period D is a sustain extinguishing period for extinguishing the illuminant electric discharge. Here, in this first conventional driving method, a reference potential of a surface electrode composed of the scan electrodes 2 and the sustain electrodes 3 is a sustain voltage Vos for sustaining the electric discharge during the sustain period C. Therefore, in connection with the scan electrode 2 and the sustain electrode 3, a potential higher than the sustain voltage Vos is called to have a positive polarity, and a potential lower than the sustain voltage Vos is called to have a negative polarity. In addition, in connection with the potential of the data electrode 5, 0V is considered to be a reference.
First, in the preliminary electric discharge period A, a positive sawtooth preliminary electric discharge pulse Vops is applied to the scan electrodes 2, and simultaneously, a negative rectangular preliminary pulse Vopc is applied to the sustain electrode 3. The pulse-height value of these preliminary electric discharge pulses is set to exceed an electric discharge starting threshold value between the scan electrode 2 and the sustain electrode 3. Accordingly, when the preliminary electric discharge pulses Vops and Vopc are applied to the corresponding electrodes, the voltage of the sawtooth preliminary electric discharge pulse Vops increases, and after a voltage between both the electrodes exceeds the electric discharge starting threshold value, a weak electric discharge occurs between the scan electrode 2 and the sustain electrode 3. As a result, a negative wall electric charge is formed on the scan electrode 2, and a positive wall electric charge is formed on the sustain electrode 3.
Succeeding to the preliminary electric discharge pulses Vops, a negative sawtooth preliminary electric discharge extinguishing pulse Vope is applied to the scan electrode 2. At this time, the potential of the sustain electrode 3 is fixed to the sustain voltage Vos. With application of the preliminary electric discharge extinguishing pulse Vope, the wall electric charge formed on the scan electrode 2 and the sustain electrode 3 is extinguished. Here, even after the wall electric charge is extinguished, space-charges such as electrons and ions and active particles such as quasi-stable particles generated in the preliminary electric discharge exists in the electric discharge space 6, even if those are a little amount. In addition, the extinction of the wall electric charge during the preliminary electric discharge period A includes adjustment of the wall electric charge in order to cause the succeeding operations such as the selection operation and the sustain electric discharge to be carried out in a good condition.
In the selection period B, after all the scan electrodes 2 are maintained at a base potential Vobw once, a negative scan pulse Vow is sequentially applied to each scan electrode 2, and a data pulse Vod corresponding to a display data is individually applied to each data electrode 5. During this period, a positive auxiliary scan pulse Vosw is applied to the sustain electrode 3. Here, the scan pulse Vow and the data pulse Vod are set to ensure that a voltage difference between confronting electrodes constituted of the scan electrode 2 and the data electrode 5 never exceeds the electric discharge starting threshold voltage when only either one of the scan pulse Vow and the data pulse Vod is applied, but exceeds the electric discharge starting threshold voltage when both the scan pulse Vow and the data pulse Vod are superposed. On the other hand, the auxiliary scan pulse Vosw is set to ensure that when the auxiliary scan pulse Vosw is superposed with the scan pulse Vow, a voltage difference between surface electrodes constituted of the scan electrode 2 and the sustain electrode 3 never exceeds an electric discharge starting threshold voltage between the surface electrodes.
Accordingly, in only the display cell applied with the data pulse Vod in time with application of the scan pulse Vow, a space electric discharge (generated between confronting electrodes) occurs between the scan electrode 2 and the data electrode 5 as shown in FIG. 15. At this time, since a voltage difference occurs between the scan electrode 2 and the sustain electrode 3 because of the scan pulse Vow and the auxiliary scan pulse Vosw applied thereto respectively, an electric discharge is triggered by the space electric discharge and is generated between the scan electrode 2 and the sustain electrode 3. This electric discharge becomes a writing electric discharge. Because a small amount of space electric charges and active particles exist in the electric discharge space 6 for the electric discharge and the extinction of the wall electric charge during the preliminary electric discharge period A, this writing electric discharge is stably generated with an electric discharge probability depending upon the amount of the existing electric charges and active particles. As a result, as shown in FIG. 15, in the selected display cell 12, a positive wall electric charge is formed on the scan electrode 2 and a negative wall electric charge is formed on the sustain electrode 3.
Thereafter, in the sustain period C, phase-inverted sustain pulses Vosp having the same pulse-height value as that of the sustain voltage Vos are supplied to all the scan electrodes 2 and all the sustain electrodes 3, respectively. The sustain voltage Vos is set to ensure that when the sustain voltage Vos is superposed on the wall voltage formed on the surface electrodes by the writing electric discharge in the selection period B, an electric discharge is generated, but when the sustain voltage Vos is not superposed on the wall voltage, no electric discharge is generated because a voltage between the surface electrodes does not exceed the electric discharge starting threshold voltage. Accordingly, the sustain electric discharge for the luminescence is generated in only the display cells having the wall electric charge formed by the writing electric discharge generated in the selection period B.
In the succeeding sustain extinguishing period D, the voltage of the sustain electrodes 3 are fixed to the sustain voltage Vos, and a negative sawtooth sustain extinguishing pulse Voe is applied to the scan electrodes 2. In this process, the wall electric charge on the surface electrodes is extinguished so that it is returned into an initial condition, namely, a condition before the preliminary electric discharge pulses Vops and Vopc are applied in the preliminary electric discharge period A. Incidentally, the extinction of the wall electric charge during the sustain extinguishing period D includes adjustment of the wall electric charge in order to cause the succeeding operations to be carried out in a good condition.
In an actual driving method for the plasma display panel, one sub-field is constituted of the preliminary electric discharge period A or the selection period B to the sustain extinguishing period D, and one field is constituted by combining a plurality of sub-fields obtained by changing the number of the sustain pulses Vosp in the sustain period C. A display luminance is adjusted by on-off selection of the respective sub-fields.
Now, a second conventional driving method will be described. FIG. 16 is a timing chart for illustrating voltage pulses applied to various electrodes in the second conventional driving method. FIGS. 17a and 17b are diagrams for illustrating a wall electric charge within the display cell in the second conventional driving method. FIG. 17a illustrates the condition of the wall electric charge in a period F, and FIG. 17b illustrates the condition of the wall electric charge in a period G. In FIG. 16, a period E is a reset period for resetting a preceding electric discharge condition and facilitating generation of an electric discharge in a succeeding selection period, and a period F is a selection period for on-off selecting the luminescence of each display cell. A period G is an electric discharge converting period for converting a space electric discharge into a surface electric discharge in a cell in which a writing space electric discharge occurs in the selection period F, and a period H is a sustain period for sustaining the illuminant electric discharge in all the selected display cells.
First, in the reset period E, a positive preliminary electric discharge pulse Vo2p is applied to the sustain electrode 3, and simultaneously, a positive preliminary electric discharge pulse Vo2pd is applied to the data electrode 5. At this time, the potential of the scan electrode 2 is fixed to 0V. The pulse-height value of the preliminary electric discharge pulse Vo2p is set to be sufficiently higher than the electric discharge starting voltage between the scan electrode 2 and the sustain electrode 3. Accordingly, with application of the preliminary electric discharge pulses Vo2pd and Vo2p, an electric discharge occurs in all the display cells, regardless of existence/non-existence of the electric discharge in the preceding sub-field, so that a large amount of wall electric charge is formed on the surface electrodes. If the application of the preliminary electric discharge pulses Vo2pd and Vo2p is terminated, a secondary electric discharge occurs because of an internal voltage generated in the electric discharge space 6 by action of the large amount of wall electric charge formed on the surface electrodes. This secondary electric discharge becomes a self-extinguishing electric discharge which will not form a new wall electric charge, since no voltage difference is given between the scan electrode 2 and the sustain electrode 3 from an external. As a result, all the wall electric charge on the surface electrodes becomes extinguished.
Next, in the selection period F, a scan pulse Vo2w is sequentially applied to each scan electrode 2, and a data pulse Vo2d corresponding to a display data is individually applied to each data electrode 5. During this period, a negative auxiliary scan pulse Vo2sw is applied to the sustain electrodes 3. As a result, as shown in FIG. 17a, in only the display cell applied with the data pulse Vo2d in time with application of the scan pulse Vo2w, a space electric discharge (generated between confronting electrodes) occurs between the scan electrode 2 and the sustain electrode 5. At this time, since the negative auxiliary scan pulse Vo2sw having the same polarity as that of the scan pulse Vo2w is applied to the sustain electrodes 3, a voltage difference enough to generate a surface electric discharge does not exist between the scan electrode 2 and the sustain electrode 3, with the result that no surface electric discharge occurs. Consequentially, as shown in FIG. 17a, a positive wall electric charge is formed on the scan electrode 2, and a negative wall electric charge is formed on the data electrode 5. But, no wall electric charge is formed on the sustain electrode 3.
Thereafter, in the electric discharge converting period G, a negative electric discharge converting pulse Vo2sd is applied to the data electrodes 5, and simultaneously, a positive electric discharge converting pulse Vo2ss is applied to the scan electrodes 2, and furthermore, a negative electric discharge converting pulse Vo2sc is applied to the sustain electrodes 3. In the cell in which the space electric discharge has occurred in the selection period F, since a wall voltage based on the wall electric charge formed by the space electric discharge is superposed on the electric discharge converting pulses Vo2sd and Vo2ss, a space electric discharge occurs again between the data electrode 5 and the scan electrode 2 as shown in FIG. 17b. In addition, a surface electric discharge is triggered by the space electric discharge thus generated, and is generated between the scan electrode 2 and the sustain electrode 3. As a result, the wall electric charge is formed on the surface electrodes as shown in FIG. 17b. 
In the succeeding sustain period H, phase-inverted sustain pulses Vosp are supplied to all the scan electrodes 2 and all the sustain electrodes 3, respectively. As a result, the sustain electric discharge for the luminescence is generated in only the display cells in which the electric discharge had occurred in the selection period F and the electric discharge converting period G.
This driving method is disclosed in for example Japanese Patent Application Pre-examination Publication No. JP-A-2000-172227.
However, in the first conventional driving method of the plasma display panel, the space electric discharge between the scan electrode 2 and the data electrode 5 and the surface electric discharge between the scan electrode 2 and the sustain electrode 3 substantially simultaneously occur in the selection period B. Therefore, a large current flows in the scan driver IC 21. In particular, when the electric discharge probability is extremely large because of a large amount of active particles existing in the display cell, the writing electric discharges substantially simultaneously occur in the display cells located on one scan electrode 2, so that a peak current attributable to the electric discharges becomes extremely large. Accordingly, a problem is encountered which requires an expensive scan driver IC having a large current capacity.
On the other hand, according to the second conventional driving method of the plasma display panel, in the selection period F, the space electric discharge occurs between the scan electrode 2 and the data electrode 5, but the surface electric discharge does not occur between the scan electrode 2 and the sustain electrode 3. Therefore, the current flowing through the scan driver IC 21 is reduced to about a half of that required in the first conventional driving method. However, the second conventional driving method is required to generate the space electric discharge using the data electrode 5 as a cathode in the electric discharge converting period G. In order to lower the electric discharge voltage in the plasma display panel, it is a general practice that, as the protection film 10 shown in FIG. 12, a film of a material such as magnesium oxide (MgO) having a high secondary electron emission coefficient is formed on an electrode functioning as a cathode, but such a material is not formed on the data electrode 5. Therefore, an extremely high voltage is required to generate the electric discharge.
In addition, as shown in FIG. 17b, when the space electric discharge is generated, since the data electrode 5 becomes the cathode, ionized electric discharge gas atoms flow into the data electrode 5 from the electric discharge space 6. As shown in FIG. 12, since the data electrode 5 is covered with the phosphor layer 8, the phosphor 8 is damaged by ions, so that luminance is deteriorated.
Furthermore, since the data electrode 5 is required to be applied with the positive pulse in the selection period F but to be applied with the negative pulse or bias in the electric discharge converting period G, the cost of the data driver IC 23 becomes increased.
Accordingly, the present invention was made to overcome the above mentioned problems. An object of the present invention is to provide a driving method of a plasma display panel capable of reducing the cost of the drivers and others without giving an adverse influence to characteristics, such as the luminance deterioration.
The plasma display panel driving method in accordance with the present invention is a plasma display panel driving method for driving a plasma display panel of a matrix display scheme which includes first and second substrates located to oppose each other, a plurality of first electrodes provided on a surface of the first substrate opposing the second substrate and extending in parallel in a row direction, a plurality of second electrodes extending in parallel to the first electrodes, each of second electrodes being paired with a corresponding one of the first electrodes so that a display line is constituted by a gap between the first electrode and the second electrode adjacent to each other, a plurality of third electrodes provided on a surface of the second substrate opposing the first substrate and extending in a column direction extending orthogonally to an extending direction of the first and second electrodes, and one display cell provided at each intersection between the first and second electrodes and the third electrodes, wherein a display is controlled on the basis of whether or not an electric discharge had occurred between the first electrode and the third electrode during an addressing period, the plasma display panel driving method comprising, during said addressing period, the step of applying a voltage generating a space electric discharge, between the first electrode and the third electrode in the display cell to be displayed, while maintaining a potential of the second electrode at a first potential which does not generate a surface electric discharge between the first electrode and the second electrode, and the step of changing the potential of the second electrode in the display cell to be displayed, to a second potential which generates the surface electric discharge between the first electrode and the second electrode.
In the present invention, during the addressing period, the current peak of the space electric discharge and the current peak of the surface electric discharge are shifted from each other in time series. Therefore, the maximum current peak value can be greatly reduced. Accordingly, even if an inexpensive scan driver IC having a small current capacity is used, a good display can be realized, and the cost can be reduced.
In addition, it is preferred that a time for maintaining the potential of the second electrode at the first potential is 0.5 to 50 microseconds, and assuming that the addressing time for each display cell is xe2x80x9c1xe2x80x9d, a time for maintaining the potential of the second electrode at the first potential is 0.3 to 30.
Furthermore, the step of applying the voltage generating the space electric discharge, between the first electrode and the third electrode, can include the step of applying a displaying voltage pulse corresponding to a display data, to the third electrodes, while sequentially applying an addressing voltage pulse to the first electrodes, and the step of changing the potential of the second electrode to the second potential can include the step of changing the potential of the second electrode to the second potential during a period in which the addressing voltage pulse is applied to the first electrode in the same display cell, or after the addressing voltage pulse is applied to the first electrode in the same display cell.
Alternatively, the step of applying the voltage generating the space electric discharge, between the first electrode and the third electrode, can include the step of applying a displaying voltage pulse corresponding to a display data, to the third electrodes, while sequentially applying an addressing voltage pulse to the first electrodes, and the step of changing the potential of the second electrode to the second potential can include the step of applying a voltage pulse of the first potential to the second electrode in synchronism with or in advance to application of the addressing voltage pulse to the first electrode in the same display cell, and the step of changing and maintaining the potential of the second electrode to the second potential during a period in which the addressing voltage pulse is applied to the first electrode, or after the addressing voltage pulse is applied to the first electrode. In this case, it is preferred that a pulse width of the voltage pulse applied to the second electrode is 0.5 to 50 microseconds, or 0.3 to 30 times the pulse width of the addressing voltage pulse.
Furthermore, the step of applying the voltage generating the space electric discharge, between the first electrode and the third electrode, can include the step of applying a displaying voltage pulse corresponding to a display data, to the third electrodes, while sequentially applying an addressing voltage pulse to the first electrodes, and the step of changing the potential of the second electrode to the second potential can include the step of applying to all the second electrodes, a voltage pulse of the first potential having a pulse width narrower than that of the addressing voltage pulse, in synchronism with application of each addressing voltage pulse, and the step of maintaining the potential of the second electrode at the second potential during a period in which the addressing voltage pulse is applied.
In this case, it is preferred that a pulse width of the voltage pulse applied to the second electrode is not less than 0.5 microseconds, or 0.3 to 0.8 times the pulse width of the addressing voltage pulse.
Still further, the plurality of second electrodes are divided into a first group and a second group which are connected to separate drive circuits, respectively. The step of applying the voltage generating the space electric discharge, between the first electrode and the third electrode, can include the step of applying a displaying voltage pulse corresponding to a display data, to the third electrodes, while sequentially applying an addressing voltage pulse to the first electrodes, and the step of changing the potential of the second electrode to the second potential can include the step of maintaining the potential of all the second electrodes included in the first group at the first potential only during a time period shorter than the pulse width of the address voltage pulse, in synchronism with application of the addressing voltage pulse to the first electrode provided in the display cell including one electrode of the second electrodes included in the first group, while maintaining the potential of all the second electrodes included in the second group at the second potential during the time period, and the step of maintaining the potential of all the second electrodes included in the first group at the second potential during a second time period after the first mentioned time period of maintaining at the first potential, while maintaining the potential of all the second electrodes included in the second group at the first potential during the second time period, so that phase-inverted voltages are applied to the first group of second electrodes and the second group of second electrodes, respectively. In this case, it is preferred that a time period for maintaining the second electrode at the first potential during the period in which the addressing voltage pulse is applied to the first electrode, is not less than 0.5 microseconds, or is not less 0.3 times the pulse width of the addressing voltage pulse. In addition, the method can further include the step of utilizing an electric power stored in a capacitance component of one group of the first group of second electrodes and the second group of second electrodes, for charging the second electrodes of the other group, in response to the voltage inversion.